linux-kernel - Re: [PATCH v2] arch/x86: Fix boot_cpu

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Date:   Tue, 31 Jul 2018 11:46:09 +0000
From:   "Sironi, Filippo" <sironi@...zon.de>
To:     Prarit Bhargava <prarit@...hat.com>
CC:     "bp@...en8.de" <bp@...en8.de>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH v2] arch/x86: Fix boot_cpu_data.microcode version output


> On 31. Jul 2018, at 13:27, Prarit Bhargava <prarit@...hat.com> wrote:
> 
> I tested this on AMD Ryzen & Intel Broadwell system and dumped the
> boot_cpu_data before and after a microcode update.  On the Intel
> system I also did a fatal MCE using mce-inject to confirm the output
> from the mce handling code.
> 
> P.
> 
> ---8<---
> 
> On systems where a runtime microcode update has occurred the microcode
> version output in a MCE log record is wrong because
> boot_cpu_data.microcode is not updated during runtime.
> 
> Update boot_cpu_data.microcode when the BSP's microcode is updated.
> 
> Fixes: fa94d0c6e0f3 ("x86/MCE: Save microcode revision in machine check records")
> Suggested-by: Borislav Petkov <bp@...en8.com>
> Signed-off-by: Prarit Bhargava <prarit@...hat.com>
> Cc: stable@...r.kernel.org
> Cc: sironi@...zon.de
> Cc: tony.luck@...el.com
> ---
> Changes in v2: Use mc_amd->hdr.patch_id on AMD
> 
> arch/x86/kernel/cpu/microcode/amd.c   | 4 ++++
> arch/x86/kernel/cpu/microcode/intel.c | 4 ++++
> 2 files changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/microcode/amd.c b/arch/x86/kernel/cpu/microcode/amd.c
> index 0624957aa068..63b072377ba4 100644
> --- a/arch/x86/kernel/cpu/microcode/amd.c
> +++ b/arch/x86/kernel/cpu/microcode/amd.c
> @@ -537,6 +537,10 @@ static enum ucode_state apply_microcode_amd(int cpu)
> 	uci->cpu_sig.rev = mc_amd->hdr.patch_id;
> 	c->microcode = mc_amd->hdr.patch_id;
> 
> +	/* Update boot_cpu_data's revision too, if we're on the BSP: */
> +	if (c->cpu_index == boot_cpu_data.cpu_index)
> +		boot_cpu_data.microcode =  mc_amd->hdr.patch_id;
> +
> 	return UCODE_UPDATED;
> }
> 
> diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
> index 97ccf4c3b45b..256d336cbc04 100644
> --- a/arch/x86/kernel/cpu/microcode/intel.c
> +++ b/arch/x86/kernel/cpu/microcode/intel.c
> @@ -851,6 +851,10 @@ static enum ucode_state apply_microcode_intel(int cpu)
> 	uci->cpu_sig.rev = rev;
> 	c->microcode = rev;
> 
> +	/* Update boot_cpu_data's revision too, if we're on the BSP: */
> +	if (c->cpu_index == boot_cpu_data.cpu_index)
> +		boot_cpu_data.microcode = rev;
> +
> 	return UCODE_UPDATED;
> }

There may be a chance of skipping this code, I think.

If the microcode is loaded on the hyperthread sibling of the boot cpu
before being loaded on the boot cpu, the boot cpu will exit earlier
from apply_microcode_intel() - in if (rev >= mc->hdr.rev) { ... }.

(This seems to be possible in apply_microcode_amd() as well.)

In my tree with the aforementioned change - Intel only - I also had
the following patch:

diff --git a/arch/x86/kernel/cpu/microcode/intel.c b/arch/x86/kernel/cpu/microcode/intel.c
index 97ccf4c3b45b..4bc869e829eb 100644
--- a/arch/x86/kernel/cpu/microcode/intel.c
+++ b/arch/x86/kernel/cpu/microcode/intel.c
@@ -797,6 +797,7 @@ static enum ucode_state apply_microcode_intel(int cpu)
        struct microcode_intel *mc;
        static int prev_rev;
        u32 rev;
+       enum ucode_state ret;
 
        /* We should bind the task to the CPU */
        if (WARN_ON(raw_smp_processor_id() != cpu))
@@ -817,9 +818,8 @@ static enum ucode_state apply_microcode_intel(int cpu)
         */
        rev = intel_get_microcode_revision();
        if (rev >= mc->hdr.rev) {
-               uci->cpu_sig.rev = rev;
-               c->microcode = rev;
-               return UCODE_OK;
+               ret = UCODE_OK;
+               goto out;
        }
 
        /*
@@ -848,10 +848,12 @@ static enum ucode_state apply_microcode_intel(int cpu)
                prev_rev = rev;
        }
 
+       ret = UCODE_UPDATED;
+out:
        uci->cpu_sig.rev = rev;
        c->microcode = rev;
 
-       return UCODE_UPDATED;
+       return ret;
 }
 
 static enum ucode_state generic_load_microcode(int cpu, void *data, size_t size,

which prevents the issue.

> -- 
> 2.17.0
> 
> 

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